Laser beam alignment and transport system

ABSTRACT

A system is disclosed for aligning a high-power laser apparatus to transmit a high-power beam along an optimum beam path to an adjustable remote beam receiver and for aligning the beam receiver for optimum reception of the high-power beam. A low-power visible laser is directed along the path to be followed by the high-power laser and a viewer such as a video camera is used for rough alignment. A pellicle, a partially reflecting mirror, and three low-power beam detectors are used with the low-power laser to align the beam transmitter with the beam receiver. Alignment of the beam receiver with the beam transmitter is checked by a high-power laser beam alignment checking system. This alignment checking system employs an annular beam detector mounted near the beam transmitter and a second beam detector mounted near the beam receiver. A beam intensity reducer is used to reduce the intensity of the high-power beam for use in alignment since prolonged direct contact by a full-power beam with the detectors would damage the detectors. A method for aligning the laser beam transmitter and receiver is also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to copending application Ser. No. 821,675,filed herewith in the names of W. H. Kasner et al. and entitled "LaserWelding of a Sleeve Within A Tube" and to Ser. No. 821,674, filedherewith in the names of P. J. Hawkins et al. and entitled "LaserWelding Head For Sleeve-To-Tube Welding".

BACKGROUND OF THE INVENTION

This invention relates to welding apparatus and more particularly towelding apparatus for welding a sleeve within a tube using a laser beam.

In tube-type heat exchangers, a first fluid flows through the tubes ofthe heat exchanger while a second fluid surrounds the outside of thetubes such that heat exchange occurs between the two fluids.Occasionally, one of the tubes can become defective such that a leakoccurs therein which allows the fluids to mingle. When this occurs, itis sometimes necessary to either plug the tube so that the fluid doesnot flow through the tube or repair the tube, thereby preventing leakagefrom the tube.

In nuclear reactor power plants, the tube-type heat exchangers arecommonly referred to as steam generators. When a defect occurs in a tubeof a nuclear steam generator that allows the coolant in the tube tomingle with the coolant outside of the tube, a more significant problemarises. Not only does this situation create an ineffective heatexchanger, but it also creates a radioactive contamination problem.Since the fluid flowing in the tubes of the nuclear steam generator isgenerally radioactive, it is important that it not be allowed to leakfrom the tubes and contaminate the fluid surrounding the tubes.Therefore, when a leak occurs in a nuclear steam generator heat exchangetube, the heat exchange tube must either be plugged or repaired so thatthe coolant does not leak from the tube. This prevents contamination ofthe fluid surrounding the tubes.

There are several methods known in the art for repairing heat exchangetubes; however, many of these methods are not applicable to repair ofheat exchange tubes wherein the tube is not readily accessible. Forexample, in a nuclear steam generator the physical inaccessibility ofdefective heat exchange tubes and the radioactive nature of theenvironment surrounding the heat exchange tubes present unique problemsto repairing heat exchange tubes that do not normally exist in otherheat exchangers. For these reasons, special methods have been developedfor repairing heat exchange tubes in nuclear steam generators.Typically, the method used to repair a heat exchange tube in a nuclearsteam generator is one in which a metal sleeve having an outsidediameter slightly smaller than the inside diameter of the defective tubeis inserted into the defective tube and attached to the defective tubeto bridge the defective area of the tube. This type of repair method isgenerally referred to as "sleeving". Previous sleeving development workhas been concerned with obtaining a relatively leakproof joint betweenthe sleeve and the tube by brazing, arc welding, explosive welding, orother joining means. Due to the need for cleanliness, close fittings,heat applications, and atmospheric control, these metallurgical bondingtechniques have problems which are not easily solvable in areas such asa nuclear steam generator where human access is limited.

In the braze sleeving methods such as the one described in U.S. patentapplication Ser. No. 790,010, filed Oct. 22, 1985, in the name of W. W.Cheng and entitled "Improved, Continuous Movement Brazing Process",which is assigned to the Westinghouse Electric Corporation, it isnecessary to heat a braze metal to its melting point in order to formthe braze bond between the sleeve and tube. One way to heat the brazematerial is by inserting a heating apparatus, such as the one describedin U.S. patent application Ser. No. 720,107, filed Apr. 4, 1985 in thename of W. E. Pirl et al. and entitled "Improved Braze Heater Assemblyand Method", which is assigned to the Westinghouse Electric Corporation,inside the sleeve within the tube. This process utilizes specially madesleeves provided with a recess containing braze material, carefulexpansion of the portion of the sleeve containing the braze materialinto contact with the tube wall, and precise positioning of the heatingapparatus within the sleeve at the site of the braze material, all ofwhich are hampered by the inaccessibility of the work area.

Welding methods for internally welding sleeves to tubes in heatexchangers require specially designed welding equipment. One suchapparatus is described in U.S. Pat. No. 4,510,372, which issued Apr. 9,1985, in the name of R. M. Kobuck et al. and is entitled "Sleeve-To-TubeWelder", which is assigned to the Westinghouse Electric Corporation.With such a device, care must be taken to avoid arc piercing the sleeveand tube.

Laser welding is an attractive alternative to arc welding and brazingfor joining metals since it is faster and produces a smaller heataffected zone. However, spatial constraints have heretofore preventedthe use of laser welding for sleeve-to-tube welding of nuclear steamgenerator tubes due to the bulkiness of lasers capable of deliveringsufficient power for welding. The invention described herein presents amethod and apparatus for such welding.

SUMMARY OF THE INVENTION

The invention is a laser beam alignment system for aligning a high-powerlaser to transmit a high-power beam along an optimum beam path to anadjustable beam receiving means and for aligning the beam receivingmeans for optimum reception of a high-power beam. The alignment systemincludes a first laser for projecting a high-power beam along a firstpath, a second laser for projecting a second low-power visible laserbeam substantially along the first path coincident with the first beam,a first adjustable reflecting means for directing the first and secondbeams along the second path corresponding to the optimum beam path whenthe first reflecting means is optimally adjusted, a first viewing meansfor viewing the remote beam receiving means to roughly align the firstreflecting means to direct the second beam generally along the optimumbeam path, a pellicle means removably mounted in the second path forsplitting the second beam into two beams, one beam continuing along thesecond path and the other beam being directed along a third path, afirst beam detector means positioned proximate the pellicle means andoperative to detect a second beam directed substantially along theoptimum beam path and redirected by the pellicle means along the thirdpath, a second beam detector means positioned proximate the remote beamreceiving means for detecting a second beam directed to the beamreceiving means substantially along the optimum beam path, a partiallyreflecting mirror means attached to the beam receiving means between thesecond detector means and the pellicle means for directing, when theremote beam receiving means is substantially optimally aligned, aportion of the second beam traveling generally along the optimum beampath substantially back along the optimum beam path to the pelliclemeans while permitting the balance of the second beam to continue alongthe optimum beam path to the second beam detector means. The pelliclemeans is operative to intercept a portion of the second beam travelingback to the pellicle means substantially along the optimum path from thepartially reflecting mirror means and to reflect the portion along afourth path. The alignment system further includes a third beam detectormeans positioned proximate the pellicle means and operative to detectlow-power beam traveling along the fourth path from the pellicle means.Each of the first and second beam detector means are operative to send asignal when contacted by the second beam. The simultaneous sending ofthe signal by the first and second beam detector means indicates thatthe first reflecting means is aligned for direction of the second beamsubstantially along the optimum beam path, the alignment of the firstreflecting means with the remote beam receiving means using the secondbeam acts to roughly align the first reflecting means with the remotebeam receiving means for reflection of the high-power beam along theoptimum beam path. The third detector means is operative to send asignal when contacted by the second beam and is useful is aligning theremote beam receiving means for optimum reception of the low-power beam.The alignment of the beam receiving means for optimum reception of thelow-power beam acts to roughly align the beam receiving means foroptimum reception of a high-power beam.

The signals sent by each of the first, second and third detector meanssare indicative of the position from the center of each detector meansthat is being contacted by the beam to enable centering of the beam oneach detector by adjusting the first reflecting means and the remotebeam receiving means. A second viewing means is provided for viewing thepellicle means to roughly align the adjustable beam receiving means andthe attached partially reflecting mirror means to reflect the portion ofthe beam which contacts the partially reflecting mirror meanssubstantially back along the optimum beam path and into contact with thepellicle means. The alignment system further includes a secondadjustable reflecting means mounted in the first path for interceptingthe first and second beams and for directing the beams to the firstreflecting means along a second portion of the first path. A first andsecond motor means are operative to adjust the first and secondreflecting means respectively to center the low power beam on the firstand second detector means, respectively. The pellicle means and secondbeam detector means are movable out of the second path.

A third movable reflecting means is provided for intercepting ahigh-power beam directed along the optimum path and for redirecting thehigh-power beam along a fifth path for use by a laser tool. A thirdmotor means is provided for moving the beam receiving means, a partiallyreflecting mirror means attached thereto, and the third reflecting meanshoused therein in response to the signal from the third beam detectormeans to center the low-power laser beam on the third detector meansafter reflection substantially back along the optimum beam path by thepartially reflecting mirror means and redirection to the third detectormeans by the pellicle means, the centering of the low-power beam on thethird detector means acting to align the third reflecting means foroptimum reception of the high-power beam when directed along the optimumpath.

The laser alignment system also includes a high-power beam alignmentchecking apparatus having an annular high-power beam detector meansremovably positioned in the second path proximate the second reflectingmeans for detecting a beam passing therethrough and for sending a signalindicative of the position of the beam passing therethrough relative tothe center of the annular detector means. The alignment checkingapparatus also has a second high-power beam detector means removablymounted near the beam receiving means for detecting a high-power beamdirected substantially along the optimum beam path into contacttherewith and for sending a signal indicative of the contact point ofthe beam on the second high-power detector means with respect to thecenter thereof. When positioned in the beam path, a partially reflectingmirror means is operative to reflect a portion of the high-power beamsubstantially back along the optimum beam path and the annular detectormeans is operative to detect this portion to check for optimum alignmentof the beam receiving means with a beam directed along the optimum beampath indicated by passage of the high-power beam portion back throughthe center of the first annular detector means.

Focusing lens means are provided near each of the first, second andthird low-power detector means for focusing low-power beam portionsdirected thereto to permit more precise beam contact position detectionthereby. The first, second and third detector means are of thepyroelectric type.

A laser beam alignment checking system is described for checking thealignment of a high-power laser beam. This checking system includes anannular beam detector means mounted near a laser beam transmitting meansfor detecting a beam passing therethrough along a beam path and forsending a first signal indicative of the position of the laser beampassing therethrough relative to the center of the annular beam detectormeans, a partially reflecting mirror means removably mounted near theremote beam receiving ,eams in the beam path for reflecting a firstportion of the beam substantially back along the beam path when the beamreceiving means is properly aligned and for permitting the remainingportion of the beam to continue along the beam path, and a secondhigh-power beam detector means mounted near the remote beam receivingmeans for detecting a beam traveling along the beam path or, if thepartially reflecting mirror means is in place in the beam path, fordetecting the remaining portion of the beam passing therethrough, andfor sending a second signal indicative of the position with respect tothe center of the second high-power beam detector means being contactedby the high-power beam. The annular beam detector means, after beingused for aligning the beam passing through its center, is also used todetect the first portion of the beam which was directed substantiallyback along the beam path and through the center thereof and to send asecond first signal indicative of the position of the beam with respectto the center of the annular detector means. A beam intensity reducermeans is used to reduce the intensity of the high-power beam before thebeam passes through the annular detector means. The signals sent by theannular beam detector means and the second high-power beam detectormeans describe the position of the high-power beam and X-Y coordinateswith respect to their centers. The annular beam detector means and thesecond high-power beam detector means are both made up of a plurality ofthermocouples which generate a signal in response to direct contact bythe high-power beam. The beam intensity reducer means is a rotatableplate having an aperture adapted to be positioned in the high-power beampath large enough for passage of the high-power beam therethrough. Theintensity of the beam is reduced by rotating the plate with a motor andthe motor is adapted to position and maintain the aperture in the beampath.

The invention also describes a method for aligning the laser beamtransmitting and receiving means used to direct the high-power laserbeam along a first beam path for reflection by a first adjustablereflecting means along a second beam path to a remote beam receivingmeans and for optimum reception of the beam thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the invention, it isbelieved the invention will be better understood from the followingdescription, taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a schematic view in elevation of the laser welding apparatusas mounted within the steam generator with parts broken away;

FIG. 2 is a schematic view of the apparatus used to align the low-powerlaser with the high-power laser;

FIG. 3 is an enlarged elevational view of one of the preferredembodiments of the partial beam reflector and intensity reducer of FIG.2;

FIG. 4 is an enlarged elevational view of another preferred embodimentof the partial beam reflector and intensity reducer of FIG. 2;

FIG. 5 is an elevational view in perspective of the preferred beamtransmitter and beam receiving means;

FIG. 6 is an elevational view partly in cross section of the preferredbeam transmitter and beam receiving means;

FIG. 7 is an elevational view of the preferred annular detector orwander ring;

FIG. 8 is an elevational view partially in cross section and with partsbroken away of the plate, sliding base portion, and welding head;

FIG. 9 is a plan view with parts broken away of the plate and slidingbase portion;

FIG. 10 is an elevational view partially in cross section of thepreferred beam receiver;

FIG. 11 is a cross-sectional view in elevation of the preferred laserwelding head;

FIG. 12 is a cross-sectional plan view taken along the line XII--XII inFIG. 11 which depicts the focal distance maintaining means;

FIG. 13 is an elevational view of the top portion of an alternativewelding head;

FIG. 14 is a cross-sectional plan view taken along the line XIV--XIV inFIG. 13 which depicts an alternative focal distance maintaining means;

FIG. 15 is a chart depicting the delivered laser power as a function oftime;

FIG. 16 is an enlarged cross-sectional view in elevation of a plannedweld site after expansion of the sleeve into contact with the tube;

FIG. 17 is an enlarged cross-sectional view in elevation of a weldbetween a sleeve and tube according to the invention;

FIG. 18 is an enlarged cross-sectional view in elevation of two discretewelds on one end of a sleeve; and

FIG. 19 is an enlarged cross-sectional view in elevation of a helicalweld path made with three passes.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates schematically the preferred embodiments of the laserwelding system 10. The next several paragraphs provide an overview ofthe system and are followed by a more detailed description of eachcomponent thereof.

Referring now to FIG. 1, a typical nuclear steam generator comprises atube bundle containing several thousand tubes 14, the ends of only fourof which are shown in for clarity. The sleeve-to-tube laser weldingsystem 10 must be capable of accessing tubes 14 at various locationsabout the tubesheet 31 of the steam generator for welding a sleevetherein to repair defects. However, the high-power laser 18, which maybe a CO₂ laser of at least 500 W and preferably 800 W, is too bulky tobe inserted into the channelhead 20. Therefore, the laser 18 may bepositioned outside the channelhead, the high-power laser beam 22 may befed into the channelhead 20 through a manway 23, and a laser beamtransport system may be used to direct the high-power laser beam 22 fromthe laser 18 to the remote welding head 26. While many forms oftransport systems are suitable for directing the beam to the remotewelding head 26, the system depicted in FIG. 1 is preferred since itdoes not restrict the range of tubes accessible by the welding head.

The beam transport system depicted in FIG. 1 directs a high-power laserbeam 22 from a laser beam transmitting means, such as beam transmitter34, to a remote laser beam receiving means, such as beam receiver 36,with no physical connection therebetween. A laser beam alignment systemis used to align the components of the beam delivery system to directthe beam along an optimum beam path and to receive the beam at therequired angle of incidence. The laser alignment system also insuresthat the high-power beam does not improperly impinge on any componentsof the beam delivery system or of the steam generator to prevent damagewhich could thereby result. For initial rough alignment purposes, thepreferred laser beam alignment system employs a low-power HeNe laser 38or another source of visible light, low-power beam detectors 40, 42, and44, and several video cameras 45, 46, and 49 or other visual observationdevices. Next, a partial beam reflector and intensity reducer means,such as beam reducer 52, is positioned in front of the high-power laser18 for alignment thereof using high-power beam detectors which cannotwithstand prolonged direct contact with the high-power beam.

Once the laser 18 is actuated, a high-power laser beam 22 is directed toa laser beam transmitter 34 which sends the beam to a remote laser beamreceiver 36. The diameter of the beam is reduced by lenses 54 and 56 andthe beam is redirected within base portion 29 upward to welding head 26within tube 14. The beam is focused by a focusing means, preferably lens58, and directed out of the head by a mirror means, preferably mirror60, through discharge outlet 62. The beam 22 melts material from sleeve12 and fuses the interface 64 between the tube 14 and sleeve 12.Rotation of the head 26 by motor 66 results in a weld which creates aleak-tight seal between the sleeve 12 and the tube 14. Each of the majorcomponents of the laser welding system will be discussed in more detailhereinafter.

The Laser Beam Alignment and Transport System

The Laser Beam Alignment and Transport System, which is shown in FIG. 1,aligns a high-power laser beam 22 from a high power laser 18 fortransmission to and reception by remote beam receiver 36 from which thebeam is directed to a remote laser welding head 26 positioned within thetube 14 into which a sleeve 12 is to be welded. Since the laser 18employed is a high-power laser, preferably in the range of 400 to 800watts, improper alignment of the high-power beam 22 could cause it tocontact and damage components of the alignment and transport system orthe steam generator. A multi-step alignment system is preferred usingfirst a visible beam from a low-power laser, such as a HeNe laser, thenthe high-power beam after it has passed through a beam intensityreducer.

FIG. 2 depicts the preferred apparatus used to direct a visible beamfrom a low-power laser 38 along the high-power laser beam path 22 foruse in aligning the high-power laser 18. In this embodiment, thelow-power laser beam 68 first contacts pellicle means, such as pellice70, which reflects a portion, preferably about 50 percent, of the beamalong a second path 72. The remaining beam portion then is reflected bysteering mirrors 74 and 76 into contact with the partial beam reflectorand intensity reducer 52. A viewing means, such as a video camera 45, ispositioned to view the low-power beam 68 through pellicle 70, whichappears semi-transparent to the light from the low-power laser 38, foradjustment of pellicle 70 for reflection of beam 68 along the properpath 72 for redirection by beam reflector 52 along the path ofhigh-power beam 22. A small opaque disk 78 is positioned betweenpellicle 70 and video camera 45 to block any low-power laser radiationscattered by pellicle means 70 toward video camera 45.

Two possible embodiments of the partial beam reflector and intensityreducer 52 are presented in FIGS. 3 and 4. In each embodiment, bothsides of the beam reducer are reflective. In addition to reflecting thebeam from the low-power laser 38 along the path of the high-power beam22, the beam intensity reducer 52 is also used to decrease the magnitudeof the high-power beam to a level safe for alignment purposes. Forreducing the intensity of the high-power beam, the beam intensityreducer 52 is positioned in the path of the high-power beam and isrotated by a motor (not shown). A high-power laser beam 22 will passthrough slot means, preferably similar to slots 80, of the intensityreducer 52 of FIG. 3 and through the aperture means, preferably a singleaperture 82, of intensity reducer 52 of FIG. 4 when they are alignedwith the beam path. When the slots 80 and aperture 82 are rotated out ofthe beam path, the beam strikes the reflective surface of intensityreducer 52 and is directed harmlessly to a conventional beam dump 84.

The magnitude of laser beam power passing through intensity reducer 52is dependent upon the size and orientation of the slots 80 and aperture82. The preferred range of net transmission is between 5 and 10 percent.The intensity reducer 52 of FIG. 3 is preferably provided with eightslots 80 positioned 45 degrees apart and subtending an angle of 3degrees each. Therefore, a beam passes through intensity reducer 52during 24 degrees of the 360 degree rotation for a net transmission of6.7 percent. For an 800 W laser, the reduced magnitude transmitted isabout 54 W.

FIG. 4 illustrates the preferred beam intensity reducer 52. The slots 80of FIG. 3 are herein replaced by a single aperture 82 large enough topass the entire beam. The average transmission of this intensity reducer52 is about 7 percent. The intensity reducer of FIG. 4 is preferredsince it need not be removed from the beam path during welding as isrequired of the intensity reducer depicted in FIG. 3. The aperture 82 ismerely aligned with the path and the beam can pass unimpededtherethrough.

Other beam intensity reducer geometries are possible, including multipleapertures and variously sized and oriented apertures and slots. Also,more than one reducer could be used in series.

A reflective means, such as mirror 86, within stationary housing 88directs any high or low power beam from the beam path 22 to the beamtransmitter 34 along path 90. The preferred embodiments of beamtransmitter 34 and remote beam receiver 36 are shown in FIGS. 1 and 5and schematically in FIG. 6. Any beam directed along path 90 isredirected by a first adjustable reflecting means, preferably reflector92, mounted within rotatable housing 94. The first reflector 92 directsthe beam to a second adjustable reflecting means, preferably reflector96, mounted within rotatable housing 98. A first motor 100 rotateshousing 94 containing reflector 92 with respect to stationary housing 88through gear assembly 102 and a second motor 104, only a portion ofwhich is observable in FIG. 1, rotates housing 98 containing reflector96 with respect to housing 94 through gear assembly 106. Theadjustability of reflector 92 and reflector 96 enables the beamtransmitter 34 to direct a laser beam to any position about thetubesheet 32, only a portion of which is shown in FIG. 1, where sleevingmay be required.

The remote beam receiver 36 must be adjustable in order to receive thebeam for transmission to the welding head. When the beam receiver 36 isproperly aligned, the beam from the transmitter 34 will contact anadjustable reflecting means, preferably reflector 108, mounted withinrotatable housing 110 and will be reflected to a second adjustablereflecting means, preferably reflector 112, mounted within rotatablehousing 114, which will reflect the beam into non-rotating base portion29 for reduction of the beam diameter by lenses 54 and 56 and forredirection to the laser welding head 26. Reflector 108 is adjusted whenmotor 116 rotates housing 110 with respect to housing 114 through gearassembly 118. Reflector 112 is adjusted when motor 120, only a portionof which is shown in FIG. 1, rotates housing 114 with respect to baseportion 29, through gear assembly 122.

The beam must contact reflector 108 directly in the center and at theproper angle in order to be reflected to reflector 112, through baseportions 29 and 28, and to the welding head 26. Initial alignment isperformed using a viewing means, preferably a video camera 46, mountedon housing 47, which is attached to housing 98 of beam transmitter 34and is movable therewith for viewing the position and orientation ofbeam receiver 36 through reflector 48. Next, the low-power laser 38 orother visible light source is activated, aligned as previously describedwith the path which the high-power laser will follow, and transmitted bybeam transmitter 34. Upon exiting housing 98 along path 124 the beamstrikes a pellicle means, such as pellicle 126, movably mounted onhousing 98, preferably mounted in a housing 128 slidable out of the beampath on slides 130 by a hydraulic cylinder 131. Pellicle 126 directs aportion of the beam along path 132 and into contact with dual axis beamdetector means, such as detector 40, which sends a signal identifyingthe contact point in X-Y coordinates. A signal indicative of contact bythe beam with the center of beam detector 40 denotes that the beam hasbeen properly directed by reflector 96 out of the beam transmitter 34.The balance of the beam continue along path 124. The percentage of thebeam directed along path 132 can be adjusted by substituting a pellicle126 of a different reflectivity. Preferably, about one-third of the beamis reflected along path 132.

Mounted to beam receiver 36 is a housing 134, preferably movable onslides 136 by a hydraulic cylinder 137, containing a second dual axisdetector means, such as detector 42, and a partially reflecting mirrormeans, such as partially reflecting mirror 138. A portion of the beamtraveling along path 124 passes through partially reflecting mirror 138and strikes detector 42, which sends a signal identifying the contactpoint in X-Y coordinates. A signal indicative of a center strikeindicates proper alignment while signals indicating off-center contactare used to adjust the beam transmitter 34 and receiver 36 for correctalignment. However, detector 42 cannot be used to indicate the angle ofincidence of the beam with the beam receiver 36. A portion of the beamstriking partially reflecting mirror 138 is reflected for this purpose.When the beam transmitter 34 and beam receiver 36 are properly aligned,this reflected portion will travel substantially back along path 124. Aviewing means, preferably a video camera 49, mounted on housing 50attached to housing 110 is used to observe the orientation of thereflected beam portion with respect to the beam transmitter 34 throughreflector 51. When optimally aligned, the reflected portion will travelalong path 124, contact pellicle 126, be reflected along path 140, andstrike the center of a beam deflector means, such as detector 44. Asignal from detector 44 indicating in X-Y coordinates a contact pointother than at the center is used to adjust the beam transmitter 34 andbeam receiver 36. Lenses 142, 144 and 146 may be used to focus the beambefore it contacts a detector for maximum accuracy. Filters may besubstituted for lenses 142, 144, and 146 or used in conjunctiontherewith to remove undesirable wavelengths, e.g., from backgroundlighting, before contact is made with any of the detectors 40, 42, or44. When adjustment of reflectors 92, 96, 108 and 112 has beenaccomplished by motors 100, 104, 116 and 120 operating in response tosignals from detectors 40, 42 and 44, the first phase of the alignmentprocess has been completed.

The second alignment phase employs the high-power laser 18 and requiresthat the low-power detectors 40, 42 and 44 be moved out of the way,preferably by sliding housings 128 and 134 out of beam path 124 onslides 130 and 136 by actuating hydraulic cylinders 131 and 137,respectively. The visible beam from low-power laser 38 is turned off andthe high-power laser 18 and partial beam reflector and intensity reducer52 are activated. The high-power beam, which is reduced to about 5 to 10percent of its full intensity by intensity reducer 52 is directed bymirror 86 to beam transmitter 34 and by reflectors 92 and 96 out of thebeam transmitter 34. A first high-power annular beam detector means,preferably such as annular beam detector 148, which is observable inFIG. 6 and is shown in detail in FIG. 7, is positioned at the point ofexit of the beam from housing 98 and detects whether the beam is exitingtransmitter 34 off of reflector 96 at the proper angle. Annular detector148, which is also called a wander ring, is made up of several thermaldetectors 150, preferably four, and is sized so that the beam can passthrough its center without contacting any of the detectors 150 but withonly minimal clearance between the beam and the detectors. When properlydirected out of transmitter 34, the beam does not contact any of thedetectors 150. The wander ring may be alternatively sized so that thebeam slightly contacts all of the detectors 150 when properly directed.A plate detector may be substituted for annular detector 148. The platedetector would have to be slid into beam path 124 for initial alignmentpurposes and removed for the balance of the alignment process.

A second high-power beam detector means, such as plate detector 152, ispositioned adjacent beam receiver 36 in the beam path 124 and signals inX-Y coordinates the point of contact by the beam. A center strikeindicates proper alignment. However, angular alignment must also bechecked. For this purpose, housing 134 is slid back into beam path 124to reflect a portion of the beam through partially reflecting mirror138. When optimal alignment has been achieved, the reflected beamportion will pass back through annular detector 148 with no detector 150being contacted by a beam traveling in either direction and with platedetector 152 indicating a center strike. Plate detector 152 must bepositioned between partially reflecting mirror 138 and detector 42 toavoid damage to detector 42. Housing 134 and plate detector 152 are nowslid out of beam path 124 and the laser system is properly aligned forlaser welding. Annular detector 148 can be used during welding to ensurethat the beam continues to exit transmitter 34 properly.

Since full beam power is required for welding, beam intensity reducer 52must be deactivated. Intensity reducer 52 shown in FIG. 3 must bephysically removed from the beam path. However, the preferred intensityreducer 52 of FIG. 4 need only be rotated to align aperture 82 with thebeam path and locked in place, permitting the beam to pass therethroughat full intensity.

The Laser Welding Head Apparatus

FIGS. 1, 8, 9 and 10 depict the preferred laser welding heat apparatus24. A plate 25 is positioned beneath the tubesheet 31 by a robotic arm30 which attaches to plate 25 at ring 37. Three linear potentiometers19, which are observable in FIGS. 8 and 9, send a signal when they aredepressed by contacting tubesheet 31, enabling level positioning ofplate 25 beneath tubesheet 31. The weld head 26 is aligned with thebottom of the tube 14 to be repaired and camlocks 27 are extended withinnearby tubes by cylinders 21, which may be hydraulic or pneumatic, andlocked to support the apparatus. A stationary base portion 29 isattached to plate 25 and a sliding base portion 28 rides up and down onslides 32, which are attached to plate 25, when lead screw 33 is rotatedby motor 35, causing the laser weld head 26, which is attached tosliding base portion 28, to be axially inserted into the tube 14 to theweld site. The laser beam is directed by reflector 112 into base portion29. The laser beam strikes a reflector means within base portion 29,such as reflector 113, which causes the beam to pass through lenses 54and 56 which reduce the diameter of the beam. The beam is preferably0.625 inches to 0.75 inches (15.88 to 19.05 mm) in diameter beforepassing through lenses 54 and 56 and 0.250 inches to 0.3125 inches (6.35to 7.95 mm) afterwards. The unreduced beam diameter could not beaccommodated by the laser welding head 26.

Beam receiver 36 depicted in FIGS. 1, 8, 9 and 10 can be used forwelding sleeves within most tubes in the tubesheet 31. Some tubes cannotcannot be accessed by this device since cylinder 137 would contactchannelhead 16 before the welding head 26 could be aligned with theentrance of the preselected tube to be sleeved. For welding within thesetubes, a second beam receiver (not shown) is preferably employed. Thissecond beam receiver is provided with all of the same components as beamreceiver 36. However, referring to FIG. 1, stationary base portion 29would preferably be located on the left side of sliding base portion 28rather than on the right side as depicted. Housings 110 and 114, camera49, and cylinder 137 would also extend to the left of sliding baseportion 28 as viewed in FIG. 1, enabling the welding head 26 to bealigned with the entrance of nearly all of the tubes in the tubesheet31.

The beam exits base portion 29 into sliding base portion 28 throughwindow 154, which is preferably made of zinc selenide and acts tocontain shield gas within sliding base portion 28. Within sliding baseportion 28, the beam is preferably reflected by reflector 156 to a beamdirecting means, preferably a reflector 158, which directs the beamthrough a hollow cylindrical member 160 rotatably connected to base 28which leads to the laser welding head 26 shown in detail in FIG. 11. Thebeam passes through a central hollow portion or cavity 162 withincylindrical housing 163 of welding head 26, is focused by a focusingmeans, preferably lens 58, and directed by a welding mirror means, suchas mirror 60, out of head 26 through discharge outlet 62. While awelding head having a solid cylindrical housing is preferred, a cage orother means for supporting a mirror and lens could be substituted.

The laser beam must be focused on the area to be welded. After travelingthrough the focusing lens 58 which is preferably made of zinc selenide,the beam is reflected by welding mirror 60, which is preferably madefrom silver coated copper or polished molybdenum, to the weld location.A focal distance maintaining means is required to maintain the weld head26 and the welding mirror 60 mounted therein a predetermined distancefrom the inner wall of the sleeve within the tube to keep the beamfocused on the inner sleeve wall for welding thereof. The preferredfocal distance maintaining means, which is most clearly shown by thecross section of head 26 depicted in FIG. 12, employs a ball plunger 164consisting of a spring loaded ball, preferably made of steel, and ameans for maintaining the ball plunger 164 in contact with the innerwall of the sleeve, such as a toggle arm 165 loaded against the insidewall of the sleeve by a spring 166. The toggle arm 165 is preferablymade of steel or a ceramic material to resist the high temperaturesencountered during sleeve welding. The spring 166 preferably provides1/4 to 1/2 pound of force for continually urging ball plunger 164against the inner wall of the sleeve during rotation of the weld head26, thereby maintaining the cylindrical housing 163 and the weldingmirror 60 therein a predetermined distance from the inner sleeve wall.The toggle arm 165 is limited in its range of travel by contact with anupper portion of the toggle arm 165a with a portion of cylindricalhousing 163a. The ball plunger is preferably provided with 2 to 5 poundsof force to resist movement except when severe tube restrictions areencountered.

An alternative embodiment of the focal distance maintaining means, whichis depicted in FIGS. 13 and 14, employs at least two spring loadedcompression pins 167 to urge a roller 168 into contact with the innersleeve wall. The roller 168 enables the head to be rotated within thesleeve while springs 169 within pins 167 maintain the roller 168 inengagement with the inner sleeve wall, thereby maintaining the weldingmirror 60 a predetermined distance from the inner sleeve wall forfocusing thereon by lens 58.

Inert gas, such as helium, argon or a mixture of the two, is supplied tothe welding head 26 to act as shield gas for the weld to prevent weldcontamination by oxygen, hydrogen, and other harmful contaminants. Thegas is supplied to base 28 through a line (not shown) to an inlet 170observable in FIG. 9, travels along a shield gas flow path which directsthe gas upwardly within cylindrical member 160 into cavity 162, passesagainst and about the periphery of lens 58 through gas flow passages 171into contact with mirror 60 and out of recessed aperture 172 indischarge outlet 62. The shield gas provides equally distributed coolingfor lens 58 and mirror 60 before exiting head 26.

Discharge outlet 62 opens outwardly from recessed aperture 172 in aconical or bell-shaped manner. This expanded opening from the recessedaperture 172 aids in distributing the shield gas over the weld locationand prevents smoke and gases generated by the laser welding fromobstructing the path of the laser. Ball plunger 164 maintains head 26 aslight predetermined and adjustable distance from the inner sleeve wall,providing an annulus through which smoke and gases are flushed away fromthe weld location. The small size and recessed positioning of aperture172 also serves to minimize splattering of molten metal into cavity 162and onto mirror 60 or lens 58.

The focal point of lens 58 can be changed by replacing spacers 174 and175 with different size spacers. The upper housing portion 176 can beremoved from the lower housing portion 177 after retaining screw 178 hasbeen threaded out. When assembled, the spacers and lens 58 aremaintained in position by spring 179 loaded against ledge 180 of lowerhousing portion 177. The tip 181 of upper housing portion 176 ispreferably provided with a taper 182 for ease of insertion into the endof a tube.

Head 26 may be rigidly extended from cylindrical member 160 of baseportion 28 through connector 184 attached to cylindrical housing 163.Since the sleeve must be welded near its top and bottom, with the bottomusually being within tubesheet 31 and the top being 30 to 60 incheswithin tube 14, the preferred embodiment of the weld head apparatusrequires an axial positioning means capable of positioning the head 26at various distances from the tubesheet 31. The preferred axialpositioning means contemplates the substitution of extension connectors184 of various lengths to couple cylindrical housing 163 to cylindricalmember 160 with longer connectors 184 acting to space head 26 a greaterdistance from base portion 28.

Since leak-tight welding of the sleeve to the tube requires a weld pathcircumscribing the sleeve periphery, a welding head rotating means isrequired. The preferred welding head rotating means, which is observablein FIGS. 8 and 9, employs a motor means, such as motor 66 attached tobase portion 28 through motor mount 186. The motor means rotates weldhead 26 through a drive means such as the gear assembly describedhereinafter. Affixed to motor shaft 188 is drive gear 190, which mesheswith driven gear 192. Since driven gear 192 is fixedly attached tocylindrical member 160, which is rotatably attached to base portion 28,rotation of gear 190 through activation of motor 66 causes cylindricalmember 160 to rotate. Cylindrical housing 163 is made to rotate withcylindrical member 160 through the non-rotational connectiontherebetween or, when welding the upper sleeve joint, through theconnection provided by connector 184.

An overlapping helical weld pattern has been found to be preferred to asingle pass weld. Therefore, an advancing means for continuouslyadvancing the welding head a distance slightly less than the width ofthe weld in each revolution of the welding head is needed. The preferredadvancing means, which is observable in FIG. 8, consists primarily of abushing 194 non-rotatably attached to base portion 28 and havinginternal threads which engage external threads about a portion ofcylindrical member 160. This screw-type advancing mechanism translatescylindrical member 160 upward or downward with respect to bushing 194and base portion 28 when cylindrical member 160 is rotated, resulting incorresponding axial movement of the welding head 26 and providing ahelical weld path.

An alternative preferred multiple pass weld consists of discrete singlepass welds closely spaced from each other. For this type of weld, anadvancing means which axially indexes the weld head a distance slightlygrater than the width of the weld is required. While not shown, such anadvancing means could be hydraulic, pneumatic, or mechanical and wouldreplace the screw-type advancing mechanism described above.

Laser Sleeve-To-Tube Welding

Due to the power losses associated with transmitting a laser beam to aremote location as well as power losses inherent in optical systems, itis recommended that the laser 18 be located as near to the workpiece aspossible. Since access to the steam generator of a nuclear plant isrestricted, most high-power lasers commercially available could not beused for sleeve-to-tube welding. Also, the minimum delivered power ofabout 500 watts rules out other available laser systems. While a CO₂laser is preferred, any laser capable of delivering 500 watts to thewelding head 26 could be used. The preferred laser will be transportableto a site adjacent the manway 24 of the steam generator 16 and willproduce an 800 watt laser beam. Such a laser is currently manufacturedby Laser Corporation of America, Wakefield, Mass.

Many different lens and mirror materials could be used in thehereinbefore described beam alignment and transport system. Thepreferred material for lenses and windows is zinc selenide. However,potassium chloride, sodium chloride, and potassium bromide are amongother known acceptable lens and window materials. The preferred mirrormaterials include polished copper, molybdenum, tungsten, or coppercoated with silver. Pellicles are preferably made of a thin plasticsheet stretched taut and coated with a partially reflective coating.However, other conventional pellicles or beam splitters can be employed.

The reflectivity of the inner wall of the sleeve at low temperaturesmakes it advisable to bring the laser up to full power immediately forfast heating of the wall to minimize reflection of the high-power beamand the potential resulting damage to the optical system components.However, abrupt shut off of the laser can have detrimental effects onthe weld. Ramping down of the laser power into the 400-500 watt rangebefore shut off has been found to minimize weld imperfections.Therefore, the preferred power curve of the laser during sleeve-to-tubewelding is as depicted in FIG. 15.

Once the laser has been set up, the robotic arm 30 has positioned thelaser welding head 26 beneath the entrance to sleeve 12 to be weldedwithin the defective tube 14, and the camlocks 27 have been actuated,the system must be aligned. FIG. 2 depicts a low-power laser 38,preferably a HeNe laser, which emits visible light useful for roughalignment purposes. The low-power beam 68 contacts pellicle 70, whichreflects a portion, preferably about 50 percent, of the beam along path72, from which it is directed by steering mirrors 74 and 76 into contactwith partial beam reflector and intensity reducer 52. The visible beamis observable by video camera 45, around opaque disk 78 and throughpellicle 70, which appears semi-transparent to the low-power beam. Thevideo camera 45 is useful in adjusting pellicle 70 to reflect beam 68along the proper path 72 for reflection by beam reflector 52 alonghigh-power beam path 22.

After striking a reflective portion of reflector 52, the preferredreflector being depicted in FIG. 4 and an alternative reflector beingdepicted in FIG. 3, the low-power beam is directed along high-power beampath 22. The beam 68 is then directed by mirror 86 within stationaryhousing 88 along path 90 to beam transmitter 34 as observable in FIG. 1.A first adjustable reflector 92, within rotatable housing 94 reflectsthe beam to a second adjustable reflector 96, within rotatable housing98, which directs beam 68 out of beam-transmitter 34. Video camera 46 isused to observe the beam through reflector 48 for adjustment of the beamexit path to align the transmitter 34 to direct the beam to the beamreceiver 36. Motor 100 rotates housing 94 through gear assembly 102 toadjust the path of beam 68 after striking reflector 92 and motor 104rotates housing 98 through gear assembly 106 to adjust the path of thebeam after reflection by reflector 96.

The remote beam receiver 36 also comprises two rotatable housings 110and 114 within which are mounted adjustable reflectors 108 and 112.Motors 116 and 120 rotate housings 110 and 114 through respective gearassemblies 118 and 122. Mounted in the optimum beam path is a partiallyreflecting mirror 138. A video camera 49 is mounted on housing 50attached to housing 110 to view transmitter 34 through reflector 51.

Once the visible laser 38 has been actuated and aligned by video camera45 for reflection by reflector 52 along beam path 22, the beamtransmitter 34 and receiver 36 can be roughly aligned through cameras 46and 49. Camera 46 observes the course of beam 68 after exitingtransmitter 34 and permits adjustment of reflectors 92 and 96 throughrotating housings 94 and 98 for direction of beam 68 to partiallyreflecting mirror 138. If beam receiver 36 is properly aligned for beamreception, a portion of the beam will be reflected back to beamtransmitter 34 substantially along the same path. Camera 49 is used toadjust alignment of housings 110 and 114 until the beam portion is soreflected. Housings 94 and 98 may have to be readjusted for the beam tostrike the partial reflecting mirror 138 after its repositioning.

Once roughly aligned, laser detectors are used for a more precisealignment. As beam 68 exits housing 98, it strikes pellicle 126, whichdiverts a portion of the beam along path 132. If the beam is leaving thebeam transmitter along the optimum path, the pellicle 126 will direct aportion of the beam into contact with the center of beam detector 40.Beam detector 40, which is preferably of the pyroelectric type,transmits a signal indicative in X-Y coordinates of the location of beamcontact for use in adjusting the beam exit path, such as by movingreflectors 52 or 86.

The remaining portion of the low-power beam contacts partiallyreflecting mirror 138, which permits a portion of the beam to passthrough and, when properly aligned, contact the center of detector 42.Laser detector 42, also preferably of the pyroelectric type, sends asignal indicating the strike location in X-Y coordinates for use inadjusting the receiver and transmitter to achieve a center strike ondetector 42. The remaining portion of the beam is reflected by partiallyreflecting mirror 138. When properly aligned, the beam portion willtravel substantially back along its path of transmission, contactpellicle 126, and be directed along path 140, striking detector 44 inits center. The preferably pyroelectric detector 44 also sends an X-Ysignal pinpointing the strike location for use in further adjustingtransmitter 34 and receiver 36. Lenses 142, 144 and 146 are used tofocus the beam portions on detectors 40, 42 and 44 respectively forprecise strike location capability. The detectors are accurate toapproximately 0.00014 inches (0.0036 mm).

With rough alignment by low-power laser completed, alignment with thehigh-power laser itself is preferred to ensure optimum transmission andreception of the high-power beam. Low-power laser detectors 40, 42 and44 are moved out of the beam path to prevent damage thereto. Preferably,these detectors, the pellicle 125, and the partially reflecting mirror138 are mounted in sliding housings, such as those illustrated in FIGS.1, 5, 6 and 10 as housings 128 and 134, for ease of movement alongslides 130 and 136 by hydraulic cylinders 131 and 137 respectively. Aplate detector 152 is slid into position in place of partiallyreflecting mirror 138. Beam intensity reducer 52 is rotated by a motor(not shown) and high-power laser 18 is activated. Beam intensity reducer52 permits passage of about 5 to 10 percent of the beam along path 22for use in alignment, the balance of the beam being directed to aconventional beam dump 84. Use of the laser at full power could damagecomponents, including the plate detector 152, which cannot withstand asustained direct strike thereby. However, the beam emitted by operationof the laser at a lower power setting may not behave the same as a beamat the higher setting to be used for welding, leading to an inaccuratealignment. Therefore, the beam intensity reducer is used to transmitonly a portion of the high-power beam for alignment purposes.

A second high-power laser detector, such as annular detector 148, whichis also referred to as a wander ring and appears as in FIGS. 6 and 7, isused to ensure that the beam exits housing 98 through the center ofaperture 196 and signals in X-Y coordinates the beam position. The beamthen travels along beam path 124 and contacts plate detector 152. Platedetector 152, which is preferably made up of wedge-shaped hightemperature thermocouples which meet at the center, sends a signalindicative of the X-Y position of the strike point of the beam.Partially reflecting mirror 138 is slid into beam path 124 with platedetector 152 as a back up to protect low-power detector 42. A portion ofthe high-power beam is reflected by partially reflecting mirror 138 and,when beam transmitter 34 and beam receiver 36 are optimally aligned,travels substantially back along beam path 124 and back through thecenter of annular detector 148. Detector 148 sends a signal indicativeof the position of the beam passing therethrough. Once the signals fromdetectors 148 and 152 have been used to align the beam transmitter 34and beam receiver 36 for transmission of a laser beam along an optimumbeam path and for optimum reception of the beam, alignment is completeand the high-power laser 18 is turned off.

Preferably, the intensity of the beam from high-power laser 18 is notreduced for actual welding of a sleeve within a tube. When a beamintensity reducer 52 such as the one depicted in FIG. 4 is used,aperture 82 is rotated into beam path 22 so that the beam can pass atfull intensity therethrough. If a beam intensity reducer 52 like that ofFIG. 3 is employed, it must be removed from the beam path for welding.

Motor 66 is then actuated, rotating motor shaft 188, which turnsattached drive gear 190. Driven gear 192 is rotated by drive gear 190,causing attached cylindrical member 160 to rotate. Weld head 26 rotatesthrough coupling of cylindrical housing 163 to cylindrical member 160or, when welding of the upper sleeve-to-tube joint, through coupling ofhousing 163 to cylindrical member 160 by extension connector 184. Ashielding gas, preferably helium is supplied to base portion 28 throughinlet 170, travels through hollow cylindrical member 160 to cavity 162,around the periphery of mirror 58 through apertures 171, and out ofrecessed aperture 172 of discharge outlet 62 into contact with sleeve12.

Laser 18 is then actuated at full welding power, preferably 700-800watts, as previously described. The high-power beam travels along path22, is redirected along path 90 by reflector 86, reflects off ofreflector 92 to reflector 94, is transmitted along bath path 124 toreflector 108 which reflects the beam to reflector 112 which directs thebeam into laser welding base portion 29. Reflector 113 diverts the beamthrough lenses 54 and 56 which reduce the diameter of the beam before itis redirected by reflectors 156 and 158 through hollow cylindricalmember 160 into cavity 162 within cylindrical housing 163. The beam isfocused by lens 58 and reflected out of welding head 26 through recessedaperture 172 of discharge outlet 62 into contact with sleeve 12.

FIG. 16 is an enlarged cross-sectional view of the sleeve 12 and tube 14at a planned weld site 64 near the top of sleeve 12. The sleeve isexpanded into contact with the tube at site 64 through hard rolling,hydraulic expansion, or other expansion methods. However, spring back ofthe sleeve material can lead to a slight gap at the sleeve-to-tubeinterface at site 64. While sleeve brazing operations can tolerate onlya very small range of gap size, an effective weld joint can be createdby laser welding with up to an 0.008 inch gap present. Also, brazingrequires a relatively clean surface for uniform braze flow, usuallynecessitating a honing or other cleaning operation before brazing. Aneffective laser weld joint can be produced despite significant surfaceoxidation.

Many nuclear steam generators employ Inconel tubes with thicknessesranging from 0.040 to 0.055 inches (1.02 to 1.40 mm). The preferredsleeving material for these tubes is Inconel with a wall thickness ofabout 0.040 inches (1.02 mm). A focal distance maintaining means, suchas ball plunger 164 and spring loaded toggle arm 165 depicted in FIGS.11 and 12, rotatably supports the weld head 26 within the sleeve 12 withthe outer edge 204 of housing 160 a fixed predetermined distance fromthe inner wall of sleeve 12 thereby maintaining welding mirror 60 apredetermined distance from the inner wall of sleeve 12. Lens 58 andmirror 60 cooperate to direct the high-power beam against the sleeve andto focus the beam at a point preferably 0.020 to 0.030 inches (0.51 to0.76 mm) beneath the inner sleeve wall, e.g., one-half to three-fourthsof the way through sleeve 12.

FIG. 17 represents in cross section a typical weld 198 made using theweld head apparatus. The two most important weld parameters are weldwidth 200 at the interface 64 between the sleeve 12 and tube 14 and welddepth 202 or penetration into the tube 14. The preferred weld width atinterface is at least 0.046 inches (1.17 mm) while the ideal weld depthis at least 0.025 inches (0.64 mm). To achieve these optimum weldparameters, the laser power delivered to the weld site should be between500 and 700 watts and the laser beam should travel across the weldsurface at 7.5 to 15.0 inches per minute (190.5 to 381.0 mm/min.),thereby delivering a specific energy of 2600 to 5300 joules/inch (102.4to 208.7 joules/mm). The preferred ranges are 600 to 700 watts deliveredat 10.0 to 12.5 inches/min. (254.0 to 317.5 mm/min.) which correspondsto a preferred rotational speed of weld head 26 of 4.0 to 7.5 rev./min.which could vary depending on the diameter of the tube and sleeve andthe delivered laser power. Too slow of a weld head rotation coulddeliver excessive specific energy to the weld site, which could causethe laser to burn through the tube wall. Too rapid rotation of weld head26 could prevent uniform fusion of sleeve 12 to tube 14.

The weld 198 is shielded from contamination by a shield gas, preferablyHelium, which exits weld head 26 through recessed aperture 172 and fillsthe inside of sleeve 12 and part of tube 14. The conical shape ofdischarge outlet 62 from recessed aperture 172 to the outer surface 204of weld head 26 acts to prevent molten weld pool material fromsplattering into weld head 26 through aperture 172, which would damagemirror 60 and lens 58.

A single weld pass within the sleeve creates a leak-tight joint betweenthe sleeve and tube along a weld path. However, multiple weld passes arepreferred to insure leak tightness and sufficient weld strength forreinforcement of degraded tubes. Two preferred methods of multiple passsleeve welding are depicted in FIGS. 18 and 19. FIG. 18 shows twodiscrete welds 198 in cross section, each one of which extends about theentire sleeve periphery at interface 64. After one weld path has beencompleted, the laser weld head is indexed up or down a distance greaterthan the weld width at the interface and a second pass is performed.Additional passes are not detrimental. FIG. 15 represents a weld 206made by a continuous helical weld path circumscribing the inside of thesleeve three times with each pass overlapping the previous weld at theinterface preferably by at least 0.005 inches (0.13 mm). The distinctweld roots 208 of each weld are observable. Two or more rotations may berequired for a helical weld of acceptable width at interface 64. A thirdpreferred embodiment would have two or more discrete weld passes whichoverlap at interface 64 by at least 0.005 inches (0.13 mm). While thewelds thusly produced would appear in cross section similar to the weldsof FIG. 19, the weld passes would not be helical in this embodiment. Allthree of the multiple weld pass types described above produce acceptablewelds. As depicted in FIG. 15, the laser power is ramped down to about500 watts delivered before the laser is shut off.

After one end of the sleeve has been welded to the tube, the weld headmust be indexed within the tube to join the other end of the sleeve tothe tube. Under the preferred method of indexing of the weld head 26 tothe end of the sleeve farther within tube 14, an extension connector 184of a predetermined length is inserted between the cylindrical housing163 and cylindrical member 160 and acts raise the welding head 26 withinthe tube as required. Following welding of each end of the sleeve, theweld head is removed from tube 14 by robotic arm 30 and repositionedwithin the next tube which requires repair for sleeve welding therein.

While preferred embodiments of the invention have been disclosed herein,many modifications thereof are possible. This invention should not berestricted except insofar as is necessitated by the spirit of the priorart.

We claim:
 1. A laser beam alignment system for aligning a high-powerlaser to transmit a high-power beam along an optimum beam path to anadjustable remote beam receiving means and for aligning the beamreceiving means for optimum reception of a high-power beam thereby, saidlaser beam alignment system comprising:a first laser for projecting whenactivated a first high-power beam along a first path; a second laser forprojecting when activated a second low-power visible laser beamsubstantially along the first path coincident with the first beam; afirst adjustable reflecting means for directing the first and secondbeams along a second path, the second path corresponding to the optimumbeam path when the first reflecting means is optimally adjusted; firstviewing means for viewing the remote beam receiving means to roughlyalign said first reflecting means to direct the second beam generallyalong the optimum beam path; pellicle means removably mounted in thesecond path for splitting the second beam into two low-power laserbeams, one beam continuing along the second path and the other beambeing directed along a third path; a first beam detector meanspositioned proximate said pellicle means and operative to detect alow-power laser beam directed substantially along the optimum beam pathand redirected by said pellicle means along the third path; a secondbeam detector means positioned proximate the remote beam receiving meansfor detecting a second beam directed to the beam receiving meanssubstantially along the optimum beam path; a partially reflecting mirrormeans attached to the remote beam receiving means between said seconddetector means and said pellicle means for directing, when the remotebeam receiving means is substantially optimally aligned, a portion ofthe second beam traveling generally along the optimum beam pathsubstantially back along the optimum beam path to said pellicle meanswhile permitting the balance of the second beam to continue along theoptimum beam path to said second beam detector means; said pelliclemeans being operative to intercept the portion of the second beamtraveling back to said pellicle means substantially along the optimumbeam path from said partially reflecting mirror means and to reflect theportion along a fourth path; and a third beam detector means positionedproximate said pellicle means and operative to detect a low-power beamtraveling along the fourth path from said pellicle means; each of saidfirst and second beam detector means being operative to send a signalwhen contacted by the second beam, the simultaneous sending of a signalby said first and second beam detector means indicating that said firstreflecting means is aligned for direction of the second beamsubstantially along the optimum beam path, the alignment of said firstreflecting means with said remote beam receiving means using the secondbeam acting to roughly align said first reflecting means with the remotebeam receiving means for reflection of the first high-power beam alongthe optimum beam path, and said third detector means being operative tosend a signal when contacted by said second beam, said third detectormeans being useful in aligning the remote beam receiving means foroptimum reception of the low-power beam, the alignment of the beamreceiving apparatus for optimum reception of the low-power beam actingto roughly align the beam receiving apparatus for optimum reception of ahigh-power beam.
 2. The laser alignment system according to claim 1,further comprising second viewing means adapted for viewing saidpellicle means to roughly align the adjustable beam receiving means andsaid attached partially reflecting mirror means to reflect the portionof the beam which contacts said partially reflecting mirror meanssubstantially back along the optimum beam path and into contact withsaid pellicle means.
 3. The laser alignment system according to claim 2,wherein the signals sent by each of said first, second and thirddetector means is indicative of the position from the center of eachdetector means that is being contacted by the beam to enable centeringof the beam on each detector means by adjusting said first reflectingmeans and the remote beam receiving means.
 4. The laser alignment systemaccording to claim 3, further comprising a second adjustable reflectingmeans mounted in the first beam path for intercepting the first andsecond beams and for directing the first and second beams to said firstreflecting means along a second portion of the first path.
 5. The laseralignment system according to claim 4, further comprising a first motormeans for adjusting said first reflecting means and a second motor meansfor adjusting said second reflecting means, said first and second motormeans being operative to adjust said first and second reflecting meansfor centering the low-power beam on said first and second beam detectormeans.
 6. The laser alignment system according to claim 5, wherein saidpellicle means and said second beam detector means are movable out ofthe second path.
 7. The laser alignment system according to claim 6,wherein the remote beam receiving means comprises a third movablereflecting means for intercepting a high-power beam directed along theoptimum path and for redirecting the high-power beam along a fifth pathfor use by a laser tool.
 8. The laser alignment system according toclaim 7, wherein the remote beam receiving means further comprises athird motor means for adjusting the beam receiving means, said partiallyreflecting mirror means attached thereto, and said third reflectingmeans in response to the signal from said third beam detector means tocenter the low-power laser beam on said third beam detector means afterreflection substantially back along the optimum beam path by saidpartially reflecting mirror means and redirection to said third detectormeans by said pellicle means, the centering of the low-power beam on thethird beam detector means acting to align said third reflecting meansfor optimum reception of a high-power beam directed along the optimumpath.
 9. The laser alignment system according to claim 8, furthercomprising a high-power beam alignment checking means, said alignmentchecking means comprising an annular high-power beam detector meansremovably positioned in the second path proximate said second reflectingmeans for detecting a beam passing therethrough and for sending a signalindicative of the position of the beam passing therethrough relative tothe center of said annular beam detector means.
 10. The laser alignmentsystem according to claim 9, wherein said beam alignment checking meansfurther comprises a second high-power beam detector means removablymounted proximate said beam receiving means for detecting a high-powerbeam directed substantially along the optimum beam path into contacttherewith and for sending a signal indicative of the contact point ofthe beam on said second high-power beam detector with respect to thecenter of said second high-power detector means.
 11. The laser alignmentsystem according to claim 10, wherein said partially reflecting mirrormeans is operative to reflect a portion of the high-power beamsubstantially back along the optimum beam path from the beam receivingmeans and said annular beam detector means is operative to detect theportion of a high-power beam reflected back by said partially reflectingmirror means to check for optimum alignment of the beam receiving meanswith a beam directed along the optimum beam path indicated by passage ofthe high-power beam portion back through the center of said annular beamdetector means.
 12. The laser alignment system according to claim 3,further comprising a first focusing lens means mounted proximate saidfirst detector means in the third path for focusing a beam directedalong the third path onto said first detector means to permit moreprecise beam contact position detection thereby, a second focusing lensmeans mounted proximate said second detector means in the second path onthe opposite side of said partially reflecting mirror means from saidpellicle means for focusing the portion of the low-power beam passingthrough said partially reflecting mirror means onto said second detectormeans to permit more precise beam contact position detection thereby,and a third focusing lens means mounted proximate said third detectormeans for focusing a beam directed along the fourth path onto said thirddetector means to permit more precise beam contact position detectionthereby.
 13. The laser alignment system according to claim 12, whereinsaid first, second and third detector means are of the pyroelectrictype.
 14. A laser beam alignment checking system for checking thealignment of a high-power laser beam transmitting means with a remotebeam receiving means, said laser beam alignment checking systemcomprising:an annular beam detector means mounted proximate the laserbeam transmitting means for detecting a high-power laser beam passingtherethrough along a beam path and for sending a first signal indicativeof the position of the laser beam passing therethrough relative to thecenter of said annular beam detector means; a partially reflectingmirror means removably mounted proximate the remote beam receiving meansin the beam path for reflecting a first portion of the beamsubstantially back along the beam path when the beam receiving means isoptimally aligned and for permitting the remaining portion of the beamto continue along the beam path; and a second high-power beam detectormeans mounted proximate the remove beam receiving means for detecting abeam traveling along the beam path and when the partially reflectingmirror means is in place in the beam path, for detecting the remainingportion of the beam passing therethrough, and for sending a secondsignal indicative of the position with respect to the center of saidsecond high-power beam detector means being contacted by the high-powerbeam; said annular beam detector means, after being used for aligningthe beam passing through its center, also being operative to detect thefirst portion of the beam directed substantially back along the beampath and passing through the center of said annular detector means andto send a second first signal indicative of the position of passage ofthe first beam portion with respect to the center of said annulardetector means.
 15. The laser beam alignment checking system accordingto claim 14, further comprising a beam intensity reducing means forreducing the intensity of the high-power laser beam before the beampases through said annular beam detector means.
 16. The laser beamalignment checking system according to claim 15, wherein the firstsignal sent by said annular beam detector means and the second signalsent by said second high-power beam detector means describe the positionof the high-power beam in X-Y coordinates with respect to the centers ofsaid annular and said second high-power beam detector means.
 17. Thelaser beam alignment checking system according to claim 16, wherein saidannular beam detector means comprises a plurality of thermocouples whichgenerate a signal indicative of the position of the beam in response toheat generated by direct contact with the high-power beam.
 18. The laserbeam alignment system according to claim 17, wherein said secondhigh-power beam detector means comprises a plurality of wedge-shapedthermocouples which meet at the center of said second detector means.19. The laser beam alignment checking system according to claim 18,wherein said beam intensity reducing means comprises a rotatable platehaving an aperture adapted to be positioned in the beam path, theaperture being large enough for passage of the high-power laser beamtherethrough, said intensity reducing means permitting passage of thehigh-power beam only through the aperture.
 20. The laser beam alignmentchecking means according to claim 19, said beam intensity reducing meansfurther comprising a motor for rotating the plate to reduce theintensity of the high-power beam for alignment purposes and for rotationof the aperture into the beam path and for maintenance of the aperturein the beam path for passing the high-power laser beam unimpeded throughthe aperture.
 21. A method for aligning a laser beam transmitting meansused to direct a high-power laser beam along a first beam path forreflection by a first adjustable reflecting means along a second beampath with a remote beam receiving means adapted to receive a beamdirected along the second beam path and for aligning the beam receivingmeans for optimum reception of a beam directed along the second beampath, said method comprising:transmitting a low-power laser beam from alow-power laser along the first beam path, the lower power beam beingreflected by the first adjustable reflecting means along the second beampath to the remote beam receiving means; intercepting the low-power beamalong the second beam path near the first reflecting means with apellicle means, the pellicle means being operative to split thelow-power beam into two portions with a first portion being redirectedalong a third path generally transverse to the second path and thesecond portion continuing along the second path; viewing the remote beamreceiving means with a viewing means to roughly align the second portionof the beam traveling along the second path with the remote receivingmeans by adjusting the first reflecting means; detecting the firstportion of the beam with a first beam detector means mounted generallyin the third path, the first beam detector means being operative todetect a beam coming in contact therewith and to send a signal inresponse to the contact; intercepting the second portion of the beamwith a partially reflecting mirror means mounted proximate the remotebeam receiving means, reflecting a third portion of the low-power beamsubstantially back along the second path with the partially reflectingmirror means, the third portion of the low-power beam being reflected bythe pellicle means along a fourth beam path substantially transverse tothe second beam path, the partially reflecting mirror means permitting afourth portion of the low-power beam to continue along the second beampath; detecting the fourth portion of the low-power beam with a secondbeam detector means mounted generally in the second beam path on theopposite side of the partially reflecting mirror means from the pelliclemeans, the second beam detector means being operative to detect a beamcoming in contact therewith and to send a signal in response to thecontact; detecting the third portion of the low-power beam with a thirdbeam detector means mounted generally in the fourth beam path andoperative to detect a beam coming in contact therewith and to send asignal in response to the contact; and moving the first reflecting meansand the beam receiving means until a signal is sent by the first, secondand third detector means simultaneously.
 22. The laser beam alignmentmethod according to claim 21, further comprising a laser beam alignmentchecking method for checking the alignment of the laser beamtransmitting means with the laser beam receiving means using thehigh-power laser beam.
 23. The laser beam alignment method according toclaim 22, further comprising deactivating the low-power laser andremoving the pellicle means, partially reflecting mirror means, andsecond beam detector means from the second beam path.
 24. The laser beamalignment method according to claim 23, further comprising reducing theintensity of the high-power beam with a beam intensity reducing means.25. The laser beam alignment method according to claim 24, furthercomprising detecting the portion of the reduced intensity high-powerbeam reflected by the first adjustable reflecting means with an annularbeam detector means positioned proximate the first adjustable reflectingmeans, the annular beam detector means being operative to send a signalindicative of the position of the beam passing therethrough with respectto the center of the annular beam detector means.
 26. The laser beamalignment method according to claim 25, further comprising detecting theportion of the reduced intensity high-power beam directed towards thebeam receiving means with a second high-power beam detector meanspositioned proximate the beam receiving means, the second high-powerbeam detector means being operative to send a signal indicative of theposition of the second detector means contacted by the beam with respectto the center of the second beam detector means.
 27. The laser beamalignment method according to claim 26, further comprising directing aportion of the reduced intensity high-power beam back to the beamtransmitting means with a partially reflecting mirror means positionedproximate the beam receiving means, detecting the portion of the reducedintensity high-power beam directed back to the beam transmittingapparatus with the annular beam detector means, and sending sends asignal indicative of the position of the beam with respect to the centerof the annular beam detector means as it passes back therethrough withthe annular beam detector means.